Abstract
This paper presents a fast digital zooming system for mobile consumer cameras using directionally adaptive image interpolation and restoration methods. The proposed interpolation algorithm performs edge refinement along the initially estimated edge orientation using directionally steerable filters. Either the directionally weighted linear or adaptive cubic-spline interpolation filter is then selectively used according to the refined edge orientation for removing jagged artifacts in the slanted edge region. A novel image restoration algorithm is also presented for removing blurring artifacts caused by the linear or cubic-spline interpolation using the directionally adaptive truncated constrained least squares (TCLS) filter. Both proposed steerable filter-based interpolation and the TCLS-based restoration filters have a finite impulse response (FIR) structure for real time processing in an image signal processing (ISP) chain. Experimental results show that the proposed digital zooming system provides high-quality magnified images with FIR filter-based fast computational structure.
Highlights
A digital zooming system can increase spatial resolution without a high density image sensor or a high cost optical zoom lens
To remove blurring artifacts caused by the interpolation process, the proposed restoration method performs 2D convolution using five 5 × 5 directionally adaptive truncated constrained least-squares (TCLS) filters according to the edge orientation θ as
Experimental results For evaluating the performance of the proposed digital zooming method, we used a set of standard images of size 512 × 512, and outdoor test images of size 1280 × 720 acquired by a mobile phone camera
Summary
A digital zooming system can increase spatial resolution without a high density image sensor or a high cost optical zoom lens. After estimating the edge orientation using steerable filters with edge refinement (Kang et al 2013a, b), the input LR image is adaptively interpolated along the estimated edge orientation using the directionally weighted linear or adaptive cubic-spline interpolation function.
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